1. Field of the Invention
The present invention pertains to an improved guide string arrangement and repair method for well casing wherein the casing guide string below the repair point is connected to a casing milling tool by a swivel joint to prevent unwanted decoupling of the guide string from the work string.
2. Background
In well casing repair operations it is known to utilize any elongated section of drill pipe known as a guide string for installation in a section of casing, particularly when the casing is disposed in an open hole portion of the wellbore, to facilitate locating the separated portion of the casing for repair operations and for connection to a new section of casing. The so called guide string is disposed in the portion of the casing remaining in the wellbore for locating or piloting the new section of casing and for locating or piloting a casing repair mill.
However, the guide string, which may be coupled sections of drill pipe or flush joint pipe up to several hundred feet in length will, when connected below a casing repair milling tool or the like, impose sufficient angular momentum or flywheel effect as to cause unwanted decoupling of the guide sting from the milling tool if the milling tool abruptly stops or decelerates due to rough or jagged casing edges encountered by the cutting edges of the milling tool. The present invention overcomes this problem with an improved guide string assembly and casing repair method.